Modern tractor-trailer combination vehicles require a properly functioning braking system in order to stop safely. If any portion of the braking system malfunctions, an unbalanced braking situation may result. For example, if a malfunction occurs in the trailer braking system while the tractor braking system functions normally, jack-knifing may occur. The problem is particularly acute if two or more trailers are involved in so-called “turnpike trains” in which a single tractor pulls two or three trailers.
Brake-related problems account for over half of all violations that can bring a highway transport vehicle into an out-of-service state during roadside inspections. Brake problems are also a common cause of transport vehicle accidents, and have been cited as a factor in nearly 30% of all truck related accidents by the Commercial Vehicle Safety Association. For vehicle owners or operators of these vehicles, brake problems can therefore lead to costly downtime and, in the event of an accident, possible liability and insurance expenses. In many cases, status of brake systems is assessed during roadside service inspections. These brake system inspections involve the measurement of the travel distance of the brake push rod to an accuracy level on the order of a fraction of an inch. However, it is estimated that 9% of vehicles that pass this test still have other brake issues that are difficult or impossible to detect without otherwise removing the wheel and/or dismantling the brake system and that warrant an out-of-service violation.
In the prior art, heavy duty trucks and other large vehicles are typically equipped with an air brake actuating system. The air brake actuating system applies air to a service chamber to move a diaphragm in a first direction. A push rod typically moves with the diaphragm, and the push rod is connected to a linkage that actuates the vehicle brakes. An emergency chamber is generally also attached adjacent to the service chamber, and is operable to move the push rod in the event that the air system fails. To this end, a high strength power spring is typically incorporated into the emergency chamber to actuate the push rod when there is a failure in the system air line. This spring also typically actuates the push rod when the vehicle is parked.
A brake actuator has a predetermined amount of available movement, or stroke, for the push rod. The amount of movement of the push rod required to fully actuate the brakes must be carefully monitored such that it is within the stroke of the brake actuator. The prior art has experienced situations wherein there has been an excessive amount of push rod movement for actuation of the brake system. This excessive required push rod movement can be created by any one of several factors. Typically, excessive movement is due to brake lining wear. As the brakes wear, more movement of the push rod is required to actuate the brakes. Further, as the linkages, connections, etc. between the members connecting the push rod to the brakes bend or become loose or excessively worn, additional push rod movement may be required to adequately stroke the brake. A combination of these several features may sometimes cause the amount of push rod movement required to actuate the brakes to approach the available push rod movement, or stroke, from the brake actuator. This is, of course, an undesirable situation.
The prior art has attempted to monitor the amount of push rod movement during actuation of the brake, and provide some indication to an operator of when there is excessive push rod movement. The determination of when there is excessive push rod movement is dependent upon the designed stroke, or rated stroke, of the brake actuator. In addition, an apparatus known as a slack adjuster is typically placed between the push rod and the foundation brake. The slack adjuster is incrementally adjusted to compensate for slack in the braking system and to decrease the required push rod movement. Automatic slack adjusters are now available which automatically adjust the foundation brake system.
Therefore, there is a need for a system which constantly monitors each of the brakes of a truck braking system and warns the operator when any brake is operating out of spec.
There is a further need for a system which constantly monitors each of the brakes of a truck braking system and warns the operator when any brake is operating out of spec and which identifies the brake in need of attention.
It is often uneconomical to change brakes as soon as they begin to operate out of spec. However, there must be a balance between economy and safety. Therefore, there is a need for a brake monitoring system that can be adjusted to account for the need to balance economy with safety. Such a system should warn the vehicle operator that the brakes are entering a range where they should be closely watched and change will be needed soon. Such a system should also be adjustable to be able to accommodate the capabilities and desires of the individual operator.